Morphologic determinants of hemodynamic state after ventricular septal myotomy-myectomy in patients with obstructive hypertrophic cardiomyopathy: M mode and two-dimensional echocardiographic assessment.

To define the morphologic features of the left ventricle after ventricular septal myotomy-myectomy and to elucidate the structural changes associated with a postoperative reduction in the pressure gradient, 28 patients with obstructive hypertrophic cardiomyopathy were studied with M mode and qualitative and quantitative two-dimensional echocardiography. Nine patients with a marked reduction in the pressure gradient (no or small, less than or equal to 25 mm Hg, residual basal gradient) demonstrated a marked reduction in septal thickness after surgery (23 +/- 6 to 13 +/- 4 mm; p less than .01), a concomitant increase in septal to mitral valve distance (20 +/- 2 to 30 +/- 5 mm; p less than .005), and a loss or substantial decrease in the magnitude of systolic anterior motion of the mitral valve. Two-dimensional echocardiographic results demonstrated an increase of over 100% in the cross-sectional area of the left ventricular outflow tract at onset of systole (2.2 +/- 0.6 to 5.5 +/- 3 cm2; p less than .01). In six of the patients postoperative paradoxic septal motion appeared to contribute importantly to the increased size of the outflow tract during ventricular systole. In contrast, nine patients with little or no change in the pressure gradient (residual basal gradient greater than or equal to 40 mm Hg) demonstrated a less marked decrease in septal thickness and no significant change in septal to mitral valve distance or magnitude of mitral systolic anterior motion. Furthermore, the postoperative left ventricular outflow tract area was significantly smaller in patients with residual basal gradients (3.0 +/- 1 cm2) than that in patients with no residual gradient (5.5 +/- 3 cm2; p less than .05). Ten patients with only provocable subaortic gradients after operation showed postoperative left ventricular outflow tract dimensions intermediate between those in patients with either residual basal gradient or no residual gradient. On the basis of this echocardiographic assessment of septal myotomy-myectomy, we conclude that abolition or reduction of the subaortic gradient after operation in patients with obstructive hypertrophic cardiomyopathy is largely the consequence of surgical enlargement of the left ventricular outflow tract area.